Scales and costs of habitat selection in heterogeneous landscapes

Summary Two scales of habitat selection are likely to influence patterns of animal density in heterogeneous landscapes. At one scale, habitat selection is determined by the differential use of foraging locations within a home range. At a larger scale, habitat selection is determined by dispersal and the ability to relocate the home range. The limits of both scales must be known for accurate assessments of habitat selection and its role in effecting spatial patterns in abundance. Isodars, which specify the relationships between population density in two habitats such that the expected reproductive success of an individual is the same in both, allow us to distinguish the two scales of habitat selection because each scale has different costs. In a two-habitat environment, the cost of rejecting one of the habitats within a home range can be expressed as a devaluation of the other, because, for example, fine-grained foragers must travel through both. At the dispersal scale, the cost of accepting a new home range in a different habitat has the opposite effect of inflating the value of the original habitat to compensate for lost evolutionary potential associated with relocating the home range. These costs produce isodars at the foraging scale with a lower intercept and slope than those at the dispersal scale.Empirical data on deer mice occupying prairie and badland habitats in southern Alberta confirm the ability of isodar analysis to differentiate between foraging and dispersal scales. The data suggest a foraging range of approximately 60 m, and an effective dispersal distance near 140 m. The relatively short dispersal distance implies that recent theories may have over-emphasized the role of habitat selection on local population dynamics. But the exchange of individuals between habitats sharing irregular borders may be substantial. Dispersal distance may thus give a false impression of the inability of habitat selection to help regulate population density.     

Immunochemical Characterization of Pyruvate Dehydrogenase Complex in Rat Brain

Pyruvate dehydrogenase complex (PDHC) in rat brain was studied immunochemically, using antibodies against the bovine kidney PDHC, by immunoblotting, immunoprecipitation, inhibition of enzyme activity, and enzyme-linked immunoabsorbent assay (ELISA). The immunoblots showed that the antibodies bound strongly to the alpha peptide of the pyruvate dehydrogenase (E1) component, and to the dihydrolipoyl transacetylase (E2) and the dihydrolipoyl dehydrogenase (E3) components of PDHC. A similar immunoblotting pattern was observed in all eight brain regions examined. On immunoblotting of the subcellular fractions, these PDHC peptides were observed in mitochondria and synaptosomes but not in the postmitochondrial supernatants. This agrees with other evidence that brain PDHC is localized in the mitochondria. These results, together with those from sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the immunoprecipitin, also showed that the alpha E1, beta E1, and E3 peptides of rat brain PDHC are very similar in sizes to those of the bovine kidney PDHC, being 42, 36, and 58 kD, respectively. The size of the E2 peptide, 66 kD, is different from that of bovine kidney E2, 73 kD. The relative abundance of PDHC protein in nonsynaptic mitochondria was compared by enzyme activity titration and ELISA. Both methods demonstrated that the amount of PDHC antigen in the mitochondria from cerebral cortex is greater than that in the olfactory bulb mitochondria. This is consistent with the results of the activity measurement. The ELISA also showed that the PDHCs in both mitochondrial populations are antigenically similar.(ABSTRACT TRUNCATED AT 250 WORDS)     

Satiety, hunger and regional brain content of cholecystokinin/gastrin and met-enkephalin immunoreactivity in sheep

Cholecystokinin (CCK) and met-enkephalin (MEK) related peptides have been shown to alter feeding behavior subsequent to their injection into the peripheral circulation or directly into the brains of several species. To evaluate the potential role of endogenous brain pools of these peptides in feeding, groups of sheep were sacrificed either immediately following a meal (satiated) or after various intervals of food deprivation (hungry). Content of CCK-gastrin immunoreactivity in the anterior hypothalami of satiated sheep was elevated compared to 2, 4, or 24 hours of food deprivation. Content of MEK increased progressively with longer intervals of fasting (4 and 24 hours) in the amygdala and basomedial hypothalamus, whereas olfactory bulb content decreased with a similar time course. The results support a potential role for anterior hypothalamic CCK/gastrin in behaviors of satiety, whereas MEK neurons of limbic/rhinencephalic regions appear to form part of a separate circuit gradually activated by increasing hunger. Results are discussed in terms of potential target regions of the peptides, as well as the regional levels and feeding response of sheep as compared to available data from other species.     

Beneficial effects of activated charcoal on bulblet production in tissue cultures of Muscari armeniacum

Production of bulblets of Muscari armeniacum through tissue culture is enhanced when 1 g/l activated charcoal is added to a modified Murashige and Skoog (MS) medium. Bulblet regeneration is direct from bulb scale explants with no intermediate callus growth. Bulblets can be transferred successfully to a greenhouse environment directly from aseptic culture.     

On the mechanical characterization of compact bone structure using the homogenization theory

In a previous paper (Crolet et al., 1993, J. Biomechanics 26, 677–687), a modelling of the mechanical behavior of compact bone was presented, in which the homogenization theory was the basic tool of computation. In this simulation, approximations were used for the modelling of the lamellae and the osteons: the lamella and the osteon were divided into cylindrical sectors, each sector being approximated as a parallelepiped having a periodic structure (fibrous composite for the lamella, superimposition of plates for the osteon). The present study deals with a new model without these approximations. First, it can be proved that the homogenized elasticity tensor for a lamella, which has a non-periodic structure, is obtained at each geometrical point as a homogenized tensor of a periodic problem. Similarly, for the osteonal structure, the components of the homogenized tensor are determined at each point as the result of a periodic homogenization.

The software OSTEON, which is the computational method associated with this model, allows one to obtain a better understanding of the effects of many bony parameters. The obtained results are in accordance with experimental data.     

Large scale production of recombinant mouse and rat growth hormone by fed-batch GS-NSO cell cultures

Investigations of biological effects of prolonged elevation of growth hormone in animals such as mice and rats require large amounts of mouse and rat growth hormone (GH) materials. As an alternative to scarce and expensive pituitary derived materials, both mouse and rat GH were expressed in NSO murine myeloma cells transfected with a vector containing the glutamine synthetase (GS) gene and two copies of mouse or rat GH cDNA. For optimal expression, the mouse GH vector also contained sequences for targeting integration by homologous recombination. Fed-batch culture processes for such clones were developed using a serum-free, glutamine-free medium and scaled up to 250 L production scale reactors. Concentrated solutions of proteins, amino acids and glucose were fed periodically to extend cell growth and culture lifetime, which led to an increase in the maximum viable cell concentration to 3.5×10⁹ cells/L and an up to 10 fold increase in final mouse and rat rGH titers in comparison with batch cultures. For successful scale up, similar culture environmental conditions were maintained at different scales, and specific issues in large scale reactors such as balancing oxygen supply and carbon dioxide removal, were addressed. Very similar cell growth and protein productivity were obtained in the fed-batch cultures at different scales and in different production runs. The final mouse and rat rGH titers were approximately 580 and 240 mg/L, respectively. During fed-batch cultures, the cell growth stage transition was accompanied by a change in cellular metabolism. The specific glucose consumption rate decreased significantly after the transition from the growth to stationary stage, while lactate was produced in the exponential growth stage and became consumed in the stationary stage. This was roughly coincident with the beginning of ammonia and glutamate accumulation at the entry of cells into the stationary stage as the result of a reduced glutamine consumption and periodic nutrient additions.     

A protocol for classifying regional dynamics,exemplified by using woodland birds in southeastern Australia

Abstract Communities of forest and woodland birds are usually studied intensively at only one or a few locations. This provides a perspective that perhaps emphasizes local phenomena at the expense of placing local dynamics in the context of processes operating at the landscape or regional scale. The present paper seeks to redress partially this imbalance by studying the dynamics of individual bird species among several habitat types (all Eucalyptus-dominated forests or woodlands) over the annual cycle. This regional-scale (250km), continental study reveals that species exhibit idiosyncratic dynamics of various kinds: restricted or more ubiquitous occupation of habitats and three forms of seasonal dynamics at the regional scale (resident, migrant and itinerant). By using this classificatory scheme, it becomes evident that the bird communities found in different habitats consist of diverse collections of strategists and that the level of diversity differs among habitat types. The difficulties that many field workers have had in reconciling their observations with community theory most likely reflect the underlying dynamism of bird communities, especially in the temperate regions on continents where seasonal fluxes are pronounced.     

Taxonomy of Pyramimonas obovata and other observations on the subgenus Vestigifera of Pyramimonas (Prasinophyceae, Chlorophyta)

A vestigiferan species commonly referred to as Pyramimonas obovata N. Carter has been redescribed as P. melkonianii sp, nov. Characters of this species and a further six (P. disomata Butcher ex McFadden, Hill et Wetherbee, P. mantoniae Moestrup et Hill, P. mitra Moestrup et Hill. P. moestrupii McFadden, P. aff. nephroidea McFadden, P. orientalis Butcher ex McFadden, Hill et Wetherbee) isolated from South African waters are used to define further the subgenus Vestigifera McFadden. This includes a unique chloroplast shape and basal hyaline region with stellate or cruciform vacuoles, a transitional plate-like structure in the flagellum, and a different microtubular root system. The proximal set of basal body connectives were found to be remarkably symmetrical and like those of the subgenus Trichocystis McFadden, and a duct fibre was found associated with the Id root in all currently investigated species. The validity of the larger body (box and crown) scales as taxonomic markers at a fine level is also questioned.